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Low rpm popping

Hello everyone.....great forum
I have a 1986 930 K27, Koklen intercooler 57,000 miles. Fresh rebuild 5 yrs ago at 50,000 mi.
My problem is when I first start it rpm's drop down to 600ish...and will not accelerate.
If you hit the pedal it does nothing but pop.
If I let it warm up...5 min or so. I can get the rpm's into the 2000-3000 range. Popping all the way.
After about 10 min. Its drive able with an occasional pop at low R's as soon as the boost kicks in, it runs like there is nothing wrong...very strong.
Did the cap and rotor...no help
Checked the overboost relay....no help
Seems to be fuel related but I have no hard evidence.
Any guidance would be greatly appreciated.
Thanks, Mark

Old 06-16-2016, 12:59 PM
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Turbofrog
 
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Wideband air fuel ratio meter should be mandatory on these engines. You can try small adjustments with the idle CO screw beside the metering plate.
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Old 06-16-2016, 01:06 PM
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Mixture is off. Probably too rich.
Old 06-16-2016, 04:41 PM
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I also did a full rebuild but at 68k. Mine ran just as you described. Long story of diagnosticating, it was the wur. Changed it, problem solved
Old 06-16-2016, 06:29 PM
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Sounds really lean. When you get into boost, vacuum leaks aren't a problem.

Last edited by Tippy; 06-17-2016 at 05:15 AM..
Old 06-16-2016, 07:38 PM
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Thanks to all for replying.
Yes...Smurfbus. Do you have any recommendations for a ratio meter ?
I would love to know what the _____ is going on.
Tippy, I'm thinking like you are..too lean and when it gets to boosts it jumps dumps fuel in and away we go. But without the air ratio meter who knows.
Nickyclyde WUR is probably the problem. Did you get yours rebuilt or did you buy another ?
Thanks, Mark
Old 06-16-2016, 08:06 PM
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People have mixed opinions on WB AFR meters but I use Innovate as its most accurate with no false readings when sensor starts to fail. Innovates quality have dropped after the innovator sold it so maybe plx gives you a cheaper pretty nice meters. Some repair shops have tail sniffing AFR meters or CO meters that could help too on idle.
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Old 06-16-2016, 08:37 PM
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check for air leaks first. trust me, as said, one on boost and air leak does not matter much unless you cant reach full boost.

check cold CCP....and WCP for that matter.

are you still running with the O2 sensor?

you can try removing the air cleaner, then start it cold and push down on the sensor plate to richen it up to see if it idles better cold. it could point you in the right direction.

how is your BOV plumbed? is it vented to atmosphere or plumbed back into the intake side of the turbo?
again, check for air leaks. are the Orings for the IC good. is the IC seated good/bolted down. ti will blow off. check the piping from/to the turbo.

did it just start doing this?
have you done any other work to it lately?
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 06-17-2016, 04:53 AM
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Thanks Smurf...

T77911s...
Started on its own after sitting for about 5 weeks.
IC is properly installed. O rings in tack and tight
Still have o2 sensor
not sure what CCP and WCP are ..sorry
Also BOV?
I will definitely push down on the sensor plate. If in fact it does improve what does that tell me?
Thanks, Mark
Old 06-17-2016, 05:10 AM
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cold control pressure-CCP
warm control pressure-WCP
BOV- blow off valve or diverter valve.
it vents the boost pressure when you let off the gas. some are recirculated back to the intake, some are vented to atmosphere.

if you push down on the sensor plate when started cold and it idles better, then you are too lean.
pushing down richens the mixture without any adjustments

check for power at the connector to the warm up regulator-WUR
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 06-17-2016, 11:20 AM
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T77
Yes..Yes and Yes..
The exact direction I was going.
I'll get to it on Sunday and keep you posted.
Thank you
Old 06-17-2016, 11:10 PM
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Check that both fuel pumps are running. Mine was acting similar once, couldn't handle any foot pedal when cold without "coughing". Turned out one of the pump relays was toast. Once warmed up, that symptom went away. These cars can run on one pump but not very well. Not enough volume or pressure for this antique CIS fuel system to work properly.

Get the car running, and pull one relay at a time. Should be a noticeable change in running. If not, you've found the culprit.
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Old 06-18-2016, 04:54 AM
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Hey Mark,
I pulled the red fuel relay towards the back of the car. No noticeable change.
I pulled the relay closer to the front of the car and it stalled.
Whadda u think?
Which pump is governed by the rear facing relay?
I did see a small spark when I pulled either relay.
I guess next step is to see if I have power at the fuel pumps.
Thanks
Old 06-19-2016, 10:55 AM
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Rear pump also powers wur so you would be rich until wur is heat soaked f rear pump does not get power.
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Old 06-19-2016, 12:47 PM
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Buy a new relay. As Smurfbus mentioned, loss of power to the WRU (via the rear pump relay) will cause a rich condition. Plus, having just one pump running will also result in a rich condition (the lower the pressure, the richer the run....that's what the WUR does, it controls the pressure which in turn affects the mixture).
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Old 06-19-2016, 04:23 PM
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Yes
Car is running very rich...That I can smell.
As I proceeded through the day I pulled the rear drivers side tire and inspected the rear pump. After moving the relays around, pump seems fine, but I didn't do a pressure check.
Not sure how to perform that. The first time I pulled the rear relay the car stalled but I could not get it to stall any time after that, no matter which relay I pulled.
WUR has power and a good ground.
When I press down slightly on the sensor plate rpm's go up.
Again, thanks to all for your input. I would not own this car if this website was not available
Old 06-20-2016, 07:45 AM
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I performed the fuel volume test and got well over 1200 cc for 30sec.
I am in the process of obtaining a banjo fuel pressure port from Len at Autosportengineering so I can check the pressure at the WUR.
My question is, I am heading in the right direction.
Car is very rich. Doesn't matter if wur is plugged in or not...same conditions.
After obtaining operating temp, it runs better but still hesitates at low RPM
Old 06-23-2016, 07:51 AM
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fuel volume is checked coming out of the FD in case you did not know. fuel volume will not effect mixture at idle. if it did, you would not be able to go boost if it would even run up that far.

fuel pressures control the mixture from cold to warm.
cold, the system is in open loop mode which means the O2 sensor is not used. once warm, if the O2 is connected, it goes closed loop and the O2 controls mixture below 3500 RPM.

seems very odd that it would smell rich but pushing down on the sensor plate would raise the idle.??? the popping also sounds lean.

make sure the frequency valve vibrates when the key is on.
the frequency valve controls the control pressure to adjust the mixture when in closed loop. BUT, the control pressure has to be set in the correct range and the mixture has to be set properly for the O2 to maintain the proper mixture.
if you don't have gauges, remove the WUR and check the input for a dirty screen. this can raise the CP which leans it out. I don't do much with the lambda systems and I am not sure if you can check the duty cycle of the frequency using a dwell meter on this car.

an air leak.
try creating an air leak and see if the popping gets worse.

timing and advance.
have you verified the timing is advancing both with the vacuum pot and mechanical advance,
with the vacuum, you can just swap the hoses. when you remove the retard hose the idle should go up, when you connect that hose to the advance port the idle should go up again.
the mechanical advance needs to be checked with both hoses not connected and using a timing,

try disconnecting the O2 sensor. this puts the freq valve in a default state.

just some things you can do if you cant check the control pressures,. those REALLY need to be checked.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 06-23-2016, 10:56 AM
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You have to get an AFR meter, absolutely mandatory... These cars act up all the time...

Mine did roughly what you describe... pig rich at idle, wouldnt progress, etc. find my prior threads...

AFR meter was <<<10 at idle...

I changed just about everything...

CDI/ROTOR/Tested The WUR/Fuel pumps/Relays/etc...

Condition is fixed, but I am not 100% sure what did it. Best I can tell it was a bad CDI ground or bad CDI in my case. But the WUR pressures were a bit off, and blowing out all the lines/return line to tank/etc helped too...

If I were you:

1) Buy AFR meter first ($200 well spent)
2) replace the relays for both fuel pumps, thats cheap
3) Check ground/connections for CDI
4) Change rotor (cheap)
5) buy the harbor freight master FI tester ($80), as it has all the stuff you need to check the pressures.

Without the AFR meter and HF pressure tester you are going to be replacing a lot of parts...

If you start with the AFR meter, and at idle its too lean and driving its too lean... its probably a fuel pump/clog/or relay...

If too rich at idle but better when driving, its ignition or WUR...

Last edited by bpu699; 06-23-2016 at 12:21 PM..
Old 06-23-2016, 12:18 PM
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Thanks guys.
I'm going shopping.
I'll be back

Old 06-24-2016, 06:36 AM
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